Burner locks out during operation after flame has been established, red lockout light on, furnace stops mid-cycle

Safety: Turn off power and close the oil shutoff valve before servicing. Wait for the burner to cool.

Steps:

• Check oil filter and pump: Inspect the oil filter at the tank and any inline filter near the Riello burner. Replace clogged filters. Verify that the Riello fuel pump pressure is stable (requires a pressure gauge and service manual settings).
• Clean or replace nozzle: Remove the burner assembly. Take out the nozzle and inspect for carbon or sludge. Replace with the exact Riello-specified nozzle. Do not oversize.
• Clean flame sensor: Remove the photocell and wipe the lens with a soft, lint-free cloth. Ensure the photocell wiring is tight and not damaged.
• Inspect ignition and grounding: Check ignition transformer terminals for tightness and corrosion. Verify burner chassis has a solid ground connection to the furnace frame. Tighten any loose screws.
• Check combustion air: Make sure the air intake and burner air inlet are not blocked. Clean the fan wheel if dirty.

If A02 persists, a professional should check combustion settings (air band, head position) and test the control box and pump under load.